Callback State

Parameter	Description	Type	Required
name	Unique State name. Must follow the Serverless Workflow Naming Convention	string	yes
type	State type	string	yes
action	Defines the action to be executed	object	yes
eventRef	References an unique callback event name in the defined workflow events	string	yes
timeouts	State specific timeout settings	object	no
eventDataFilter	Callback event data filter definition	object	no
stateDataFilter	State data filter definition	object	no
onErrors	States error handling and retries definitions	array	no
transition	Next transition of the workflow after callback event has been received	string or object	yes (if end is not defined)
end	Is this state an end state	boolean or object	yes (if transition is not defined)
compensatedBy	Unique name of a workflow state which is responsible for compensation of this state	string	no
usedForCompensation	If true, this state is used to compensate another state. Default is false	boolean	no
metadata	Metadata information	object	no

Example:

JSON	YAML
{ "name": "check-credit", "type": "callback", "action": { "functionRef": { "refName": "call-credit-check-microservice", "arguments": { "customer": "${ .customer }" } } }, "eventRef": "credit-check-completed-event", "timeouts": { "stateExecTimeout": "PT15M" }, "transition": "evaluate-decision" }	name: check-credit type: callback action: functionRef: refName: call-credit-check-microservice arguments: customer: "${ .customer }" eventRef: credit-check-completed-event timeouts: stateExecTimeout: PT15M transition: evaluate-decision

Serverless orchestration can at times require manual steps/decisions to be made. While some work performed in a serverless workflow can be executed automatically, some decisions must involve manual steps (e.g., human decisions). The Callback state allows you to explicitly model manual decision steps during workflow execution.

The action property defines a function call that triggers an external activity/service. Once the action executes, the callback state will wait for a CloudEvent (defined via the eventRef property), which indicates the completion of the manual decision by the called service.

Note that the called decision service is responsible for emitting the callback CloudEvent indicating the completion of the decision and including the decision results as part of the event payload. This event must be correlated to the workflow instance using the callback events context attribute defined in the correlation property of the referenced Event Definition.

Once the completion (callback) event is received, the Callback state completes its execution and transitions to the next defined workflow state or completes workflow execution in case it is an end state.

The callback event payload is merged with the Callback state data and can be filtered via the "eventDataFilter" definition.

If the defined callback event has not been received during this time period, the state should transition to the next state or end workflow execution if it is an end state.

The timeouts property defines state specific timeout settings. Callback states can define the stateExecTimeout, actionExecTimeout, and eventTimeout properties. For more information on workflow timeouts reference the Workflow Timeouts section.

Note that transition and end properties are mutually exclusive, meaning that you cannot define both of them at the same time.